Join Date: Apr 2006
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Re: Lumen rating Dr. LED "Sidekick" LED bulb E26 base
erps, as i understand it the problem is "let's confuse the customer with numbers".
Or was it the old Devo lyric, "he baffled me with science" ?
OK, if I've screwed this up someone please correct it.
Lumens reflect the brightness from a specific area. If you picture a shining white ball, a miniature sun hanging in the middle of your cabin, the light coming out of it can be measured in candela, or lumens, among other ways. Now draw a little circle or square on the surface of that sun. Measure the light coming out of that little circle. That's your lumens. Step back a few yards, hold up an incident light meter, see how much light is falling on it, and you've got candela. One is the emitted light from a specific spot, the other is the light falling on something away from the whole bulb. Under certain conditions, yes, the two will be the same. Or at least, have a linear relation. At other times, not.
Drop a towel over the back side of the sun, and your cabin now gets way dimmer. But wait, if you meaure that circle you drew again, the lumens haven't changed. Somehow, the lumens haven't changed but the sun got dimmer! And the candlepower measurement will be lower.
And there's your discrepancy, the traditional tungsten bulb puts out light in a 360-degree x/y/z axis, a whole ball of light that bounces around, some wasted, some not. The LED replacement for it often has light that is only directed to a half-sphere "down" or "out" from the bulb. If the bulb is installed in a directional application, that may be a good thing, kind of like using a reflector spotlight to get more "brightness" from the same wattage.
If you were planning to hang it on a bare wire in mid-air, not so good, because half the light isn't there.
A lot of folks are spending a lot of R&D money on LED replacements for household bulbs. I don't think they're anywhere near ready yet. Still a LOT of bucks, with a limited light pattern, from what I've seen.
BTW, this is why the COLREGS get way more clever than we give them credit for, by simply asking "Can you see it from xx miles away? over these many degrees?"